PROJECT SUMMARY/ABSTRACT It is estimated that over 15% of annual tuberculosis (TB) cases occur in individuals who are co-infected with human immunodeficiency virus type 1 (HIV-1), and that TB has caused one-third to one-half of all AIDS deaths to date. Mycobacterium tuberculosis (MTb), the causative agent of TB, exacerbates immunological failure and disease progression in HIV-1 patients. In turn, HIV-1-mediated depletion of CD4+ T lymphocyte populations significantly increases the risk of reactivation of latent TB disease. The host response to MTb infection is initiated by the pathogen binding to host cells and signaling through several receptors found in mononuclear phagocytes, including the pattern recognition receptors (PRRs) TLR2, TLR4, and TLR9, and the interleukin (IL)-1 receptor. Notably, TLR2, which acts as a costimulatory receptor on memory CD4 T+ cells, is expressed at significantly elevated levels on CD4 T+ cells from patients with active TB. These signals mediate the induction of proinflammatory cytokines, including tumor necrosis factor (TNF) and IL-6. They also activate other diverse host factors, including nuclear factor &#954;B (NF-&#954;B) and the mitogen-activated protein kinases (MAPKs) p38 and c-Jun N-terminal kinase (JNK), which are important regulators of HIV-1 replication. We have recently demonstrated that the transcription factor nuclear factor of activated T cells 5 (NFAT5) also plays an important role in constitutive and MTb-induced HIV-1 replication in monocytes and in activated CD4+ T cells. Furthermore, we have shown that induction of NFAT5 expression in MTb-infected monocytes requires signaling through the adaptor protein myeloid differentiation primary response gene 88 (MyD88). Based on these data, we hypothesize that MTb enhances HIV-1 replication in human CD4+ T lymphocytes and macrophages by inducing the expression of NFAT5 and other regulatory factors via MyD88-dependent signaling mechanisms. The robust system we have developed in our laboratory to study live MTb/HIV-1 coinfection in primary human peripheral blood cell cultures provides a powerful tool to apply to the testing of this hypothesis. In Aim 1, we will investigate the molecular and cellular mechanisms of MTb-induced, NFAT5- mediated regulation of HIV-1 replication in CD4+ T lymphocytes and monocytes. In Aim 2 we will determine the role of TLR2 in MTb-mediated regulation of HIV-1 replication in CD4+ T lymphocytes. We expect that these investigations will elucidate several biological pathways and molecular interactions that promote the reciprocal exacerbation of MTb and HIV-1 disease progression in co-infected individuals, and that our findings will provide a foundation for the development of efficacious therapeutic agents able to specifically target the pathological host response pathways that promote the progression of both infections.